Typically, the largest tables are
lyrMetricEvents
lyrCompletedRecips
clicktracking_
members_
To improve speed:
1. Remove data from the lyrMetricEvents table.
This table contains server performance data, which is added every minute. Typically this creates a huge number of rows which are only visible to the server admin. The best thing to do is run:
truncate table lyrMetricEvents
which typically removes several GBs of data.
2. Delete old mailings or lists that contain obsolete data or are otherwise unnecessary. This will remove entries from the other larger tables, and help in the export.
3. On Postgres, perform a "vacuum" on the database before exporting. This will compress the database and speed up disk operations.